People introduce exotic plants intentionally and by accident, through a variety of means. Plants are introduced for food, medicine, landscaping, erosion control, forage, windbreaks and many other purposes. Many non-native plants have great economic value for agriculture, forestry, horticulture and other industries and pose little environmental threat. The potatoes that fed Ireland originated in the South American Andes. The apples we enjoy today originated in Kazakhstan. These are seen to be ‘beneficial’ plant introductions.

Many ornamental species have escaped from plantings to become significant environmental weeds. About two-thirds of the almost 1,200 plants currently reported to be invasive in natural areas in the U.S. were imported for their horticultural value. Japanese barberry, bamboos, privets, Chinese and Japanese wisteria, porcelain-berry, Oriental bittersweet and Princess tree were introduced and planted for ornamental purposes and are now major weeds of natural habitats, requiring significant resources to attempt to control. Other

species have been introduced unknowingly on various imported products soil, water used for ship ballast or packing materials. Japanese stiltgrass, one of our most insidious invasive grasses, was used as packing material for porcelain and likely got a start when some material containing seed was deposited outdoors.

Once established in a new environment exotic species are able to proliferate and expand over large areas and become invasive pests.